Engines may utilize particulate filters in an exhaust system for reducing the amount of soot emissions by trapping soot particles. During the operation of an engine, particulate filters may be regenerated in order to decrease the amount of trapped particulate matter within the filter. However, during engine operation, exhaust gas temperatures may increase and cause damage to the particulate filter.
U.S. Pat. No. 7,640,729 describes an approach with a secondary air flow passage located upstream of a particulate filter. To regenerate the particulate filter, the disclosed method delivers a secondary air flow upstream from the particulate filter based on the particulate filter temperature and particulate matter burn off rate. Further, a temperature sensor is located downstream from the particulate filter in the exhaust passage in order to measure the exhaust gas temperature.
The Inventors have recognized a problem with streaming additional oxygen into the exhaust passage for regeneration of a particulate filter. The flow of additional oxygen into the exhaust passage via a secondary passage may occur at non-optimal times during engine operation. Further, having a temperature sensor downstream from the particulate filter may cause a delay in the shut-off of the additional oxygen flow. Further, the delay may cause an inaccurate reading of the particulate filter temperature resulting in damage to the filter.
In one example, some of the above issues may be addressed by a method comprising, regenerating a particulate filter in an engine exhaust, where burning of soot is initiated by introducing additional oxygen into the exhaust gas upstream of the particulate filter when an exhaust temperature exceeds a threshold, and a soot burn rate is controlled by adjusting pulsing of the additional oxygen introduced based on engine operation. For example, when intake boost pressure is greater than exhaust pressure, pulsed air is introduced via a high-pressure EGR passage. As such, the frequency and/or pulse-width of the additional oxygen pulses may be responsive to operating conditions by adjusting pulsing of the high-pressure EGR valve positioned in the passage. Thus, introduction of additional oxygen via pulses may allow for the soot burning process to be controlled more precisely.
In another example, a temperature sensor may be positioned inside the particulate filter of an engine exhaust passage. In this way, the temperature sensor may be able to make a more precise measurement of the exhaust gas temperature. For example, termination of additional oxygen pulses may occur once the temperature inside the particulate filter reaches a maximal threshold. Therefore, a temperature sensor positioned inside the particulate filter may allow for improved regeneration of a particulate filter.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.